1. Field of the Invention
The present invention relates to a recording element substrate, a recording head including the recording element substrate, and a recording head cartridge. More specifically, the invention relates to an ink jet recording element substrate for recording by using ink.
2. Description of the Related Art
In a recording head of an ink jet system, for example, in order to operate a plurality of heat generating resistive elements provided in the recording head at different timings, time-division driving is performed, in which the plurality of heat generating resistive elements are divided into a plurality of blocks and each of the blocks is driven in sequence.
FIG. 7 is a block diagram illustrating an example configuration of a recording element substrate 111, which includes conventional heat generating resistive elements. FIG. 7 illustrates heat generating resistive elements (heaters) H1 to H64 arrayed in a row, and switching elements T1 to T64. AND circuits A1 to A64 constitute a recording element selection circuit.
Recording data DATA input to an input terminal 107 is transferred to a shift register 104, and then transferred to a shift register 101. A latch circuit 105 latches the data of the shift register 104. A latch circuit 102 latches the data of the shift register 101.
A clock CLK for operating the shift register is input to an input terminal 110. A heat enable signal HE for controlling ON-time of the switching elements T1 to T64 from the outside is input to an input terminal 108. A latch signal LT is input to an input terminal 109. An AND circuit 103 calculates logical products of the heat enable signal HE and outputs D1 to D4 of the 4-bit latch circuit 102 to output recording data signals D1L to D4L.
The recording element substrate 111 includes a heater power (VH) input terminal for inputting a driving voltage of the heat generating resistive elements and a GND (GNDH) terminal for inputting a ground level. The recording element substrate further includes a logical power (VDD) input terminal for inputting a voltage for a logical circuit and a GND (VSS) terminal for the logical circuit.
Logical levels of the input terminals have been set to GND level by pull-down resistance. Thus, when a contact is open, a 4-bit value of the recording data (DATA) that is input to the shift register 104 becomes “0000”.
Next, a signal flow when a recording operation is performed will be described. Recording data input from a recording apparatus is input to the shift register 104, which constitutes a logical circuit, and divided into recording data signals D1L to D4L and block control signals B1L to B4L. A decoder 106 converts the block control signals into block selection signals N1 to N16. The recording element selection circuits (AND circuits) A1 to A6 receives the recording data signals D1L to D4L and the block selection signals N1 to N6, and perform logical product calculation to determine the heat generating resistive elements to be driven.
Such a recording head is mounted on a carriage of the recording apparatus. A contact pad (contact) of the recording head side and a contact pad (contact) of the carriage side are connected to each other by pressure. This connection realizes electrical connection (may simply be referred to as a contact, hereinafter) between a control unit of the recording apparatus and the recording element substrate of the recording head, thereby enabling power supplying and communication.
In the connected portion, a contact failure having no contact (hereinafter, simply referred to as contact open), or a contact failure in which adjacent contacts are electrically short-circuited (hereinafter, simply referred to as a contact short-circuit) may occur. In such a case, the recording data sent from the recording apparatus may not be correctly input to the recording head, causing deterioration in recording quality.
FIG. 9 illustrates a recording operation when the recording apparatus and the recording head are normally interconnected. FIG. 9 is a conceptual diagram illustrating the block control signals B1L to B3L during the recording operation, a time sequence of the block selection signals N1 to N6, which are decoder output values, and positions of dots on a recording medium implemented by the recording element.
Numerical values 1 to 64 of recording dots correspond to numbers of heaters belonging to a heater array 406. Values (N1 to N64) of the block selection signals, signal levels and time axes (time chart) of the block control signals, and positions of dots recorded in the recording medium correspond to one another.
FIG. 9 illustrates a recording state during 300 microseconds. In a block control signal timing-chart, at time 0, the block control signals B1L to B4L are all at low levels (L), and N1 is selected as a block selection signal. In the block N1, recording elements (nozzles) H1, H17, H33, and H49 are simultaneously driven to record a dot 1, a dot 17, a dot 33, and a dot 49.
Then, according to logical level switching of the block control signals B1L to B4L, the decoder 106 sequentially outputs block selection signals N1 to N16.
FIG. 8 is a table illustrating the recording element selection circuits A1 to A64, which become active based on combinations of the values N1 to N16 of the block selection signals, the values D1L to D4L of the recording data signals, and values of heat enable signals HE.
FIG. 10 illustrates a case where the electrical contact of the input terminal 107 is disconnected at a timing T after the start of the recording operation. In this case, as described above, because of pull-down resistance, irrespective of values of the input recording data, values of recording data (DATA) input to the shift register 104 become “0000”. Hence, values latched by the latch circuit 105 also become “0000”, causing logical levels of all of the block control signals B1L to B4L to be low.
Thus, as illustrated in FIG. 9, the block selection signals may normally be switched to N12, N13, and N14 in sequence. However, because of the disconnected electrical contact, as illustrated in FIG. 10, N1 is always selected as a block selection signal. As a result, recording is continued while the recording elements H1, H17, H33, and H49 belonging to the heater array 406 are always selected.
There is a method for detecting such a contact failure. A method discussed inn Japanese Patent Application Laid-Open No. 8-252909 calculates a logical product of all signals input to a recording element substrate, and detects a contact failure based on a result of the calculation. A method discussed in Japanese Patent Application Laid-Open No. 2000-141660 monitors a voltage supplied to a logical circuit for driving a heater, and detects a contact failure based on a result of the monitoring.
However, because of an increase in circuit size resulting from a higher density of the nozzles of the recording head and higher performance of the recording head, a circuit space for the circuit of detecting contact failures may be difficult to provide. An object of the present invention is to provide a recording element substrate, a recording head including the same, and a recording head cartridge, which improves the issue described above.